Considerable effort has been expended to develop waste heat recovery systems to recover waste heat normally exhausted in the atmosphere by industrial processing plants. Many of these systems involve heat exchange apparatuses and methods. Many of these apparatuses are used to transfer "process heat", as distinguished from waste heat, from one point in the process to another. Many of these heat exchangers utilize a liquid heat transfer medium. However, the temperatures and other conditions present in a waste heat recovery application are typically far more severe than those encountered in applications wherein process heat is being transferred.
U.S. Pat. No. 4,137,965, teaches a waste heat recovery system utilizing heat exchangers in combination with heat transfer liquids. This system also teaches temperature and pressure control means for the effective and safe recovery of waste heat.
Attempts to utilize these prior art heat recovery systems for variable temperature process heaters such as blast furnace stoves have met with difficulties. For example, in the blast furnace process because of the cyclic nature of the process, wide swings of 100.degree. or more of the exhaust gases from the blast furnace stove are a given condition. By contrast, the waste heat recovery system of U.S. Pat. No. 4,137,965 presupposes a substantially uniform temperature of the exhaust gases.